This study intends to determine whether prostaglandins might be the natural endogenous substrates of the hepatic or extrahepatic microsomal monooxygenase. Specifically, it is planned to explore the effects of in vivo alteration of monooxygenase activity (induction or inhibition) on the rate and mode of metabolism of prostaglandins in vivo and in vitro and on certain prostaglandin-mediated biological activities. Thus, the possibility that the levels and activity of prostaglandins are subject to monooxygenase controls will be investigated. Also, the question whether there are mammalian cytochrome P-450s with high affinity and specificity for prostaglandins will be examined with isolated cytochrome P-450 fractions, purified by classical means or by affinity chromatography.